1. Field of the Invention
The present invention relates to dry docks for boats. In particular the present invention relates to a dry dock which will support a boat with its hull above the waterline and which will permit lowering of the boat hull below the waterline for launching purposes.
2. Description of the Prior Art
The 1869 patent to Richardson, U.S. Pat. No. 87,291, discloses a dry dock with air-tight tanks and a screw-rod mechanism for lowering of a boat into the water and for lifting of the boat from the water. This dry dock has the disadvantage of requiring substantial mechanical forces to operate the screw-rod mechanism.
Muller patent U.S. Pat. No. 1,486,257 shows a dry dock having pontoons which may be partially flooded for tilting of the dry dock. This arrangement results in undesired tilting of a vessel supported by the dry dock.
U.S. Pat. No. 3,114,53 to Burch discloses a boat lift with float units and a pulley arrangement for lifting and lowering of the boat. This boat lift suffers from the use of a somewhat complicated pulley mechanism and the requirement of substantial mechanical forces to operate the pulley mechanism.
Roberts patent U.S. Pat. No. 3,315,627 shows a pneumatically operated floating dry dock. The employed is quite complicated requiring a number of ballast tanks, inflatable rubber bags and multiple valves for operating the tanks and bags.
A floating dry dock for small boats is disclosed in Mann patent U.S. Pat. No. 3,412,702. The Mann patent is similar to the Burch patent mentioned above in that it uses a pulley system for raising and lowering of pontoons. Again, this arrangement has the disadvantage of requiring substantial mechanical forces to operate the pulley system.
Rutter patent U.S. Pat. No. 4,018,179 shows a pontoon system for supporting watercraft on a body of water. This system requires tilting of the pontoons for carrying out a two-step procedure where the front portion of the boat is first lifted followed by raising of the rear portion of the boat.
UK patent application GB 2 005 603 A discloses a floating dock which is variably buoyant and includes a pair of central rotatably mounted caissons to which outrigger floats are attached by arms. This application mentions, but does not show or describe in detail, that working platforms can be attached to the arms. However, the nature of the keel blocks attached to the caissons is such that the platforms could not be continuous and uninterrupted in form. Moreover, the construction of the floating dock in this UK publication is further complicated because the caissons are restricted to rotation about their respective central axes.
For further background of the invention, attention is invited to the following patents: Francis U.S. Pat. No. 3,149,599; Mauritzen U.S. Pat. No. 3,610,192; Fukuda U.S. Pat. No. 3,638,437; King U.S. Pat. No. 3,895,592; and Meek et al. U.S. Pat. No. 6,131,528.
The present invention includes a dry dock advantageously employing an articulated mechanism supported by a plurality of pontoons where one or more of the pontoons may be selectively flooded with water, or filled with a fluid lighter than water, for respectively lowering a boat into the water or lifting of the boat above the waterline.
A primary object of the present invention is the provision of a dry dock of the type just described which takes advantage of buoyancy forces for lifting and lowering of a boat.
A still further object of the present invention is the provision of a variable buoyancy dry dock and boat launching apparatus having a self-contained variable buoyancy system.
Another object of the present invention is the provision of a dry dock which will support a boat with the hull of the boat completely above the waterline and which will permit lowering of the boat into the water for launching purposes.
Still another object of the present invention is the provision of a dry dock of the type described which is of simple and easy-to-manufacture construction.
These and other objects and advantages of the present invention will become apparent from the following description of preferred embodiments.